Hot water bottles: the tiny flower that says it’s time to bin yours

Turn your hot water bottle over and look closely at the rubber near the neck. Somewhere on there is a small stamped flower with a number in the middle. Most of us have never given it a second glance, but it tells you exactly how old the bottle is, and whether it might be time for a new one.

Hot water bottles are a cheap and effective way to keep warm around the house. They also carry a real health risk when things go wrong. In 2024, nearly 1,000 people in England and Wales were admitted to burn units because of hot water bottle accidents.

The health and safety training team at High Speed Training has shared its advice on using them safely.

Dr Richard Anderson, Head of Learning and Development at High Speed Training, said: “Hot water bottles are a fantastic way to beat the chill, and with energy costs remaining a concern, they are more popular than ever. However, like any household item that utilizes high heat, they aren’t without risk.”

How old is your hot water bottle?

The advice is to replace a hot water bottle every two to three years. The rubber they are made from can degrade over time, which makes an older bottle more likely to split or leak.

How to read the daisy wheel

The flower-shaped symbol is known as the “daisy wheel”, and it is embossed directly onto the neck or body of the bottle. Here is how it works:

• The number in the centre is the year the bottle was made.
• The twelve petals stand for the twelve months of the year.
• The number of segments with dots shows the month it was made.
• The number of dots in the final (or only) filled segment shows the week of that month.

So a wheel with 25 in the middle and dots in the first six segments was made in June 2025. If that last filled segment has three dots, it came off the production line in the third week of the month.

How to fill your hot water bottle safely

Before you fill up, give the bottle a proper look over for any obvious damage or wear and tear.

Then hold back on the kettle. “Avoid filling the bottle with boiling water,” Richard said. “This can damage the internal seams, so it’s best to leave it to cool before filling up. It’s also advisable to only fill the bottle about two-thirds of the way full, before expelling any remaining air and ensuring the stopper is tightened securely.”

Covers, cushions and storage

That knitted or fluffy cover does more than look cosy. Richard said: “Always use some type of cover on a hot water bottle, which helps to avoid contact burns on the skin, and avoid sitting or lying on them, as this can increase the risk of the bottle failing.”

And once you are done with it for the night, don’t leave the water sitting inside.

“When not in use, drain the bottle and store with the stopper removed in a cool, dry place like a cupboard.”